Heparin is a polydisperse, naturally occurring polysaccharide that inhibits coagulation, the process whereby thrombosis occurs. Heparin consists of unbranched polysaccharide chains of varying lengths and molecular weights. Chains of molecular weight from 5000 to over 40,000 daltons, make up pharmaceutical-grade heparin.
Heparin, derived from natural sources, mainly porcine intestine or bovine lung tissue, can be administered therapeutically for prevention and treatment of thrombosis. However, the effects of unfractionated heparin can be difficult to predict. During treatment of thrombosis with unfractionated heparin, coagulation parameters must be monitored very closely to prevent over- or under-anticoagulation.
Numerous brands of heparins and low molecular weight heparins (LMWH), such as dalteparin and enoxaparin are available for the treatments that rely on their anti-coagulant activity. A large number of in vitro and animal experimental investigations, and even clinical trials, indicate that heparin and its derivatives have beneficial properties others than those related to its anticoagulant effect. However, existing heparins and LMWH are not suitable for treating other medical conditions because of the bleeding risk associated with the anticoagulant effect. Although LMWHs represent significant clinical advantages compared to heparin, this class of substances, by definition, still retain high anticoagulant activity that can give rise to potentially life threatening side-effects.
Because it can be given subcutaneously and does not require APTT monitoring, LMWH permits outpatient treatment of conditions such as deep vein thrombosis or pulmonary embolism that previously mandated inpatient hospitalization for unfractionated heparin administration.
The LMWH dalteparin has been shown to decrease protracted labor in women receiving prophylaxis for deep venous thrombosis. The mechanism is believed to involve dalteparin-induced increased levels of interleukins resulting in a favourable inflammatory reaction that promotes ripening of the cervix. Further, dalteparin has been shown to increase contractility of the uterus (Acta Obstetricia et Gynecologica, 2010; 89:147-150).
However, heparin and LMWH are not suitable for preventing or treating such maladies for a number of reasons. First, heparin and LMWH have significant, well-known anti-coagulant effects that restrict their use in late pregnancy and during delivery, both for prophylactic and acute use, due to the bleeding risk. For example the use of dalteparin is strictly contraindicated when epidural anesthesia is given, a measure frequently taken during child birth. Second, heparin has been associated with heparin-induced thrombocytopenia, a severe immune-mediated drug reaction that can occur in any patient exposed by heparin. It is a potentially devastating prothrombotic disease caused by heparin-dependent antibodies that develop either after a patient has been on heparin for 5 or more days or if the patient has had previous heparin exposure. Another untoward possible effect of long term treatment with heparin is that it may induce demineralization of bones and cause osteoporosis.
There have been many attempts to eradicate or reduce the anticoagulant activity of heparins or low molecular weight heparins in order to provide low anticoagulant heparins (LANs) which aim to benefit from other potential clinical effects from the heparin chains than the anticoagulant effect, without carrying the risk of untoward effects associated with heparin, predominantly bleeding. However, there is limited clinical experience of this type of heparins and so far no such products are allowed for clinical use
European Patent 1059304 discloses enzymatically degraded or oxidized heparin resulting in a product with low anticoagulant effect, having an average molecular weight of 9 to 13 kDa, which is suggested for the treatment of neurodegenerative diseases.
U.S. Pat. No. 4,990,502 demonstrates one way of treating native heparin to cleave residues of the pentasaccharide residues responsible for the anticoagulant effect and a following depolymerization that results in a low anticoagulant, low molecular weight heparin with a an average molecular weight 5.8 to 7.0 kDa. In U.S. Pat. No. 4,990,502 time consuming methods, such a dialysis for about 15 hours, are used to terminate the oxidation process. Such processes could affect the molecular weight distribution of the final product. Controlling the molecular weight and the length of the polysaccharide chains is crucial to obtain the desired biological effect of the compound.
The bioavailability of long chain heparins after subcutaneous dosing is low and the possibility of heparin induced thrombocytopenia (HIT) induction is also positively correlated to the chain lengths. To reduce these clinically undesired properties the heparin derivative should not be of full length. Heparin chains of certain molecular weight can be obtained by fractionation of standard heparin. However, the production of heparin derivatives of intermediate or low molecular weight by fractionation methods such as gelfiltration, alcohol precipitation and ion exchange chromatography is associated with a significant waste of raw material as high molecular mass heparins are thus discarded.
The present invention, as outlined in the following sections describes a new process wherein the polysaccharide chains are shortened and a suitable average molecular weight distribution will be achieved favoring its clinical use and reducing the risk associated with the largest polysaccharide chains together with a minimal loss of raw material.